1. Field of the Invention
The invention relates generally to the construction of electric motors, and more particularly to systems and methods for constructing electric motors in which an expandable material is inserted into the slots in which magnet wires are positioned, and wherein the material is expanded in the slots to mechanically restrain the wires to prevent damage that might result from movement of the wires within the slots.
2. Related Art
A typical electric motor has two primary components: a rotor; and a stator. The stator is a stationary component, while the rotor is a movable component which rotates within the stator. Typically, in an AC induction motor, magnetic fields are generated in the stator and are induced into the rotor. The interaction of the magnetic fields created by the stator and the rotor cause the rotor to rotate within the stator.
The motor incorporates electromagnets that generate changing magnetic fields when current supplied to the electromagnets is varied. These electromagnets are normally formed by positioning coils (windings) of insulated wire around ferromagnetic cores. In an AC induction motor, the ferromagnetic cores are formed between “slots” in the stator core. When electric current is passed through the wire, magnetic fields are generated around the wire and consequently in the ferromagnetic cores. Changing the magnitude and direction of the current changes the magnitude and polarity of the magnetic fields generated by the electromagnets.
Electric motors that are designed for downhole applications (such as driving an electric submersible pump) are typically AC induction motors. These motors, generally speaking, are long and narrow. Usually, downhole motors are less than 10 inches in diameter, and they may be tens of meters long. This extremely elongated shape drives many aspects of a downhole motor's design. For example, because downhole electric motors are typically very long, many of these motors employ a closed-slot design which serves to confine the magnet wires within the slots of the stator. The slots are often at least partially filled with epoxy or varnish to hold the wires in position and to provide additional electrical insulation around the wires.
In very high-temperature applications, however, varnishes and epoxies may become chemically unstable and break down. When this occurs, the wires may move within the slots, allowing the wires, particularly the insulating coatings around the wires, to become damaged. Damage to the magnet wires may cause the motor itself to fail. It would therefore be desirable to provide improved systems and methods to restrain the wires within the slots in high-temperature and other applications, thereby increasing the reliability, run life and thermal capability of the motor.